1. Field of the Invention
The invention relates to a control apparatus adapted for performing teaching or simulation of operations or actions with respect to an industrial robot, a machine tool, or the like, and also relates to a control method of controlling the apparatus.
2. Description of Related Art
Conventionally, in production lines of plants, many industrial robots are used for automatically performing welding, parts assembling, transportation, and other operations. These industrial robots are taught or programmed in advance by dedicated control apparatus to perform predetermined operations or to make a series of movements or actions. Then, the industrial robots carry out various works in the production lines by repeating the content of teaching or programming. The control apparatus is generally called a “teaching apparatus”, and one example of the apparatus, which is of a portable type, is called “teach pendant”. Such teach pendants are also used for teaching or programming processing procedures to various types of machining tools, such as NC machining tools.
Normally, an operator holds such a teach pendant with one hand, and performs teaching operations by operating or manipulating input keys, or the like, with the other hand. In this case, industrial robots, NC machining tools, or the like (hereinafter generally called “machine”) to be taught or programmed to perform operations or make movements or actions step by step in accordance with the teaching operations. These operations include driving of a motor, turning of an arm(s), energization of a working head (such as a welding gun), and the like. In some cases, the apparatus performs an operation or a movement different from that intended by the teaching operator, due to a teaching error, a mechanical failure of the machine, or the like. In order to avoid danger to workers, including the operator, in the vicinity of the machine and to prevent damage to the machine, the control apparatus needs to be constructed such that teaching operations of the apparatus are inhibited or the machine is immediately stopped if any of the above dangerous situations occur.
In view of the above-described situations, a conventional teach pendant is provided with a switch called a “deadman switch”. The deadman switch is designed to establish an operation permission state in which the teach pendant is allowed to perform teaching operations and the machine is allowed to make movements only when the teaching operator holds or grips the teach pendant in his or her normal posture. For example, a two-position type deadman switch is arranged to permit the teach pendant to be operated only when the teaching operator is pressing down on the deadman switch, and to inhibit operations of the teach pendant, and eventually inhibit operations of the machine, when the teaching operator releases the deadman switch. This type of deadman switch is disposed at a position where the fingers supporting the teach pendant contact the switch. For example, a deadman switch is disposed at a position where right-hand fingers or left-hand fingers contact the reverse side of a housing of the teach pendant. Experimentally, the teaching operator tends to release the teach pendant at the moment that he/she is surprised by, or feels danger, caused by an abnormality in the operation (e.g., movements) of the machine for some reason. In view of this tendency, the teach pendant is inhibited from being operated or the machine is stopped when the deadman switch is turned off, thus assuring improved safety.
In other cases, people tend to grip a nearby object hard when they are surprised. If the operator grips the teach pendant 10 hard when he/she is surprised at an abnormality in the operation of the machine, the two-position type deadman switch is held in the ON state, and cannot inhibit the operation of the teach pendant 10. To deal with this situation, a three-position type deadman switch has been proposed. The deadman switch of this type permits the operation of the teach pendant 10 only when a switch portion is pressed down with a predetermined pressure, and inhibits the operation of the teach pendant 10 when the deadman switch is released or gripped hard. Thus, the three-position type deadman switch ensures higher safety and is more highly recommended in view of the typical behavior of human beings. Use of the three-position deadman switch is mandatory in certain locales and circumstances.
However, the teaching operator may perform a teaching (input) operation with the right hand while holding the teach pendant with the left hand, or may perform a teaching (input) operation with the left hand while holding the teach pendant with the right hand. In addition, the operator may hold the teach pendant first with one hand and then with the other hand, namely, the operator may switch bands for holding the teach pendant, since his/her fingers or arms may get tired during a long-term teaching operation. In view of these situations, the teach pendant may be provided with two deadman switches, namely, one at a position where the left-hand fingers touch the pendant, and the other at a position where the right-hand fingers touch the pendant. In these cases, the two dead switches are arranged to function independently to allow the teach pendant to perform operations.
As described above, when the teaching operator is surprised, he/she does not necessarily release the teach pendant, but may grip hard the teach pendant as one of nearby objects. At this time, if the teach pendant has two deadman switches, one for the left hand and one for the right hand, as described above, one of the deadman switches may be gripped hard, and the other deadman switch may be gripped softly (in a normal operating state with a predetermined pressure). In this case, since the deadman switch that is gripped softly is made effective, the teach pendant and the machine to be programmed are kept operating or moving. Thus, in spite of the provision of the deadman switches, the teaching pendant is not smoothly shifted to an operation inhibited state when it falls into an abnormal state different from the normal state. Meanwhile, when two three-position type deadman switches are disposed, it may be possible to provide a mechanical or electrical changeover switch that enables the teaching operator to select which deadman switch should be made effective. It is, however, necessary to perform a switching operation with the changeover switch each time the hand holding the teach pendant is replaced by the other hand during normal work, resulting in poor handling and reduced efficiency.